1. The act of prolonging something
   - prolongation, protraction, perpetuation

1. Make longer
   "Lengthen this skirt, please" 
2. Become long or longer
   "In Spring, the days lengthen"

Type of: continuance, continuation, grow, increase

Antonym: shorten

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• database management system
• datable
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• dataset
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• date of reference
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• dated